Such cooling plates are arranged on the inside of the furnace shell and have internal cooling ducts. These cooling plates are connected via connection pieces projecting from their back to a cooling system of the shaft furnace outside the furnace shell. Their surface facing the interior of the furnace is generally lined with a refractory material.
Most of these cooling plates are still made from cast iron. As copper has a far better thermal conductivity than cast iron, however, there is a current trend towards the use of cooling plates made from copper or copper alloys. Meanwhile several production methods have been proposed for copper cooling plates.
Initially an attempt was made to manufacture copper cooling plates by mould casting like cast iron cooling plates, the internal cooling ducts being formed by a sand core in the mould. This method has not proved effective in practice, however, because the cast copper plates exhibit cavities and porosity far more frequently than cast iron cooling plates. However, it is well known that such cavities and porosity have an extremely negative effect on the life and thermal conductivity of the plates.
It is already known from GB-A-1571789 how to replace the sand core by a preformed metallic pipe coil made from copper or high-grade steel in mould casting of the cooling plates. The pipe coil is integrally cast in the cooling plate body in the mould and forms a helical cooling duct. The two ends of the pipe coil project as connection pieces from the cooling plate body. This method has also not proved effective in practice. A high heat transmission resistance exists between the copper cooling plate body and the integrally cast pipe coil, so that relatively poor cooling of the plate results. Furthermore, cavities and porosity in the copper can likewise not be effectively prevented with this method.
Copper cooling plates for metallurgical furnaces are known from DE 29611704 U1, according to which prefabricated coolant ducts, consisting of copper pipe sockets, copper pipe lines and copper pipe bends are integrally cast in the cooling plate. The complete, prefabricated copper conduit is placed into the casting mould and the molten copper is poured around it. An improvement in heat transmission is expected for as a result of a partial fusing of the molten copper and the pipe wall. However, this process also fails to provide any protection from cavities and porosities in the cast copper plate.
A cooling plate made from a forged or rolled copper ingot is known from DE-A-2907511. The cooling ducts in this case are blind holes, which are introduced into the rolled copper ingot by mechanical deep drilling. The blind holes are sealed by soldering or welding in threaded plugs. Connecting holes to the blind holes are drilled from the back of the plate. Connection pieces for coolant feed or return are subsequently inserted in these connecting holes and soldered or welded in. Finally, pipe connection pieces with a larger diameter are welded or soldered as spacers coaxially with the connection pieces on the back of the plate.
The subsequently published WO 98/30345 describes a method in which a preform of the cooling plate is continuously cast. Inserts in the casting duct of the continuous casting mould produce ducts running in the continuous casting direction, which form straight cooling ducts in the finished cooling plate. The cross-section of these integrally cast ducts preferably has an oblong shape with its smallest dimension at right angles to the cooling duct. Consequently cooling plates with a smaller plate thickness than cooling plates with drilled ducts can be manufactured. Copper is thus saved and the useful volume of the furnace increased. A further advantage of the oblong cross-section is that larger exchange areas on the coolant side can be achieved in the cooling plate. A plate is cut out of the continuously cast preform by two cuts at right angles to the casting direction, two end faces with a spacing corresponding to the required length of the cooling plate being formed. In the next production step connecting holes terminating in the ducts are drilled into the plate at right angles to the rear surface and the end terminations of the ducts closed. Connection pieces are subsequently inserted in the connection holes, as already described above.
The methods described in DE-A-2907511 and WO98/30345 both permit production of high-grade cooling plate bodies from copper or copper alloys, the method described in WO98/30345 being characterised by particularly low production costs. However, a disadvantage of the finished cooling plates of both methods compared to cooling plates with integrally cast pipe coils or mould-cast plates is that they exhibit a relatively high pressure loss in the area of the transitions from the connection pieces to the cooling ducts. This applies in particular, but not exclusively, if the cooling ducts have an oblong cross-section, as described in WO98/30345.
For the sake of completeness it should also be mentioned that a cast-iron cooling plate with integrally cast cooling pipes, which has an oval cross-section in its straight section, but a circular cross-section at the inlet and outlet, is described in EP-A-0144578.